1. Field of the Invention
The present invention relates to an electronic device and more particularly to a small-sized electronic device having storage and backup functions such as a small electronic memorandom.
2. Description of the Related Art
This type of small-sized conventional electronic device is arranged so that when a battery for supplying the device body with electricity is replaced, the change-over to a backup power source is effected and the contents of a RAM are not erased. For the backup power source, a supplementary battery or a capacitor has been conventionally used. A microprocessor installed in the electronic device typically incorporates a clock circuit. The clock circuit invariably in an operating state, and hence the electric power supplied from the backup power source is consumed in this clock circuit.
After removing the battery from the device body for replacement the above-mentioned electronic device using the capacitor as the backup power source, the contents of the RAM are held by capacities accumulated in the capacitor. For this reason, the electric current consumed by the clock circuit presents a problem. More specifically, the clock circuit consumes the capacities accumulated in the capacitor in a short period of time. Thereby a problem arises since the time for holding the contents of RAM is shortened. An additional problem is that if the capacitor is arranged in a large configuration to retain the RAM contents for a long time, the size of the electronic device body is dominated by the capacitor so that a compact device body cannot be attained.
An improvement of a memory protect circuit is disclosed in Japanese Published Unexamined Patent Application No. 63-15346. The memory protect circuit is provided with a power source change-over unit that is capable of changing the power source supplied to the memory to an auxiliary power source. However, this reference does not, disclose an arrangement which extends the time for backing up the memory contents by stopping the clock circuit.